Medium carbon steel is 0.25% ~ 0.60% carbon, carbon steel, the hot working and cutting performance is good, poor welding performance.

 

According to the chemical composition of steel could be divided into two types: carbon steel and alloy steel.Carbon steel is divided into: (1) low carbon steel, carbon content less than 0.25%;(2) the medium carbon steel, carbon content is 0.25% - 0.6%;(3), high carbon steel, carbon content is more than 0.6%;Medium carbon steel hot working and cutting performance is good, poor welding performance.Strength and hardness is higher than low carbon steel and the plasticity and toughness lower than that of low carbon steel.Without heat treatment, direct use of hot rolled, cold drawn material, can be used after heat treatment.The medium carbon steel after quenching and tempering has good comprehensive mechanical properties.To achieve the highest hardness about HRC55 (HB538), sigma b for 600 ~ 600 mpa.So in a moderate level of a variety of purposes, medium carbon steel is the most widely used, except as building materials, also used in the manufacture of various kinds of machinery parts.

 

(1) preheating is helpful to reduce the highest hardness of medium carbon steel heat affected area, prevent to produce cold crack, this is the main technological measures, the welding of medium carbon steel preheating can also improve the joint plasticity, reduce the residual stress after welding.Usually, 35 and 45 steel preheating temperature is 150 ~ 250 ℃ carbon thickness and stiffness is very big, no matter how high or cracks tend to be large, can preheat temperature up to 250 ~ 250 ℃.

 

(2)If welding is too big, overall preheating have difficulty, can undertake local preheating, local heating heating in the range of joint on each side of 150 ~ 200 mm.

2 electrode preferable alkaline electrode when conditions permit.

 

(3) the welding groove form an open U type groove welding should be carried out as far as possible.If it is a casting defects, digging out the groove shape should be smooth, its purpose is to reduce the ratio of parent metal melting into the weld metal, in order to reduce the carbon content in the weld seam, to prevent the crack.

 

(4) due to the parent metal melting welding process parameters to the first layer of weld metal in the proportion of up to 30%, so the first layer seam welding, should use small current, welding speed slow, as far as possible to reduce the parent metal penetration.

 

5] after welding heat treatment after welding butt welding best thing immediately to eliminate stress, heat treatment, especially for the large thickness of welding, high rigid structure and severe working conditions (dynamic load and impact load) of the welding .Eliminating stress tempering temperature is 600 ~ 650 ℃. If unable to eliminate stress after welding, heat treatment shall be carried out immediately after heat treatment.